Curing Method Employing UV Sources That Emit Differing Ranges of UV Radiation

ABSTRACT

A UVLED apparatus (and related system and method) provide efficient curing of an optical-fiber coating on a drawn glass fiber. The apparatus employs one or more UV-radiation sources that emit electromagnetic radiation to effect the curing of coated glass fiber.

CROSS REFERENCE TO PRIORITY APPLICATION

This application claims the benefit of U.S. Patent Application No. 61/351,205 for a “Curing Apparatus Having UV Sources That Emit Differing Ranges of UV Radiation” (filed Jun. 3, 2010), which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present invention embraces an apparatus, a system, and a method for curing coatings on drawn glass fibers.

BACKGROUND

Glass fibers are typically protected from external forces with one or more coating layers. Typically, one or more coating layers (e.g., two or three coating layers) are applied during the optical-fiber drawing process (i.e., whereby a glass fiber is drawn from an optical preform in a drawing tower). A softer inner coating layer typically helps to protect the glass fiber from microbending. A harder outer coating layer typically is used to provide additional protection and to facilitate handling of the glass fiber. The coating layers may be cured, for example, using heat or ultraviolet (UV) light.

UV curing requires that the coated glass fiber be exposed to high intensity UV radiation. Curing time can be reduced by exposing the coating to higher intensity UV radiation. Reducing curing time is particularly desirable to permit an increase in fiber drawing line speeds and thus optical-fiber production rates.

As will be understood by those having ordinary skill in the art, curing occurs when UV radiation is absorbed by photoinitiators in the glass-fiber coating. After absorbing UV radiation, the photoinitiators decompose into free radicals, which promote the polymerization of the glass-fiber coating.

One of the problems of conventional UV-curing methods and devices, however, is that oxygen interferes with the polymerization of the glass-fiber coating by reacting with the free radicals. Therefore, a need exists for a UV-curing apparatus that is capable of curing glass-fiber coatings with improved curing efficiency.

SUMMARY

Accordingly, the present invention embraces an apparatus (and associated systems and methods) for curing in situ optical-fiber coating with UV radiation.

An exemplary apparatus for curing a coated glass fiber includes a cavity that defines a curing axis along which a glass fiber having an incompletely cured coating may pass. The glass fiber's coating usually possesses one or more absorption peaks, which typically occur at wavelengths greater than 300 nanometers. Typically, a protective tube that is substantially transparent to UV radiation surrounds the curing axis. A first UV-radiation source is positioned within the cavity. Typically, at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 200 nanometers and 300 nanometers. A second UV-radiation source is also positioned within the cavity. Typically, at least 80 percent (e.g., 90 percent) of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths greater than 300 nanometers. In addition, at least 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths within a 20-nanometer range (e.g., a 10 nanometer range).

An exemplary method for curing a coating on a glass fiber includes applying a coating to a glass fiber and then passing the coated glass fiber through a cavity (e.g., along the cavity's curing axis). The glass fiber's coating typically has a first absorption peak occurring at a wavelength greater than about 300 nanometers (e.g., greater than 350 nanometers). Moreover, the glass fiber typically does not possess a coating having an absorption peak that is between about 200 nanometers and 300 nanometers. UV radiation is directed from a first UV-radiation source to promote the curing of the coating (i.e., the coating is exposed to UV radiation). Typically, at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 200 nanometers and 300 nanometers. UV radiation is also directed from a second UV-radiation source to promote the curing of the coating. Typically, at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths within 10 nanometers of the coating's first absorption peak.

The foregoing illustrative summary, as well as other exemplary objectives and/or advantages of the invention, and the manner in which the same are accomplished, are further explained within the following detailed description and its accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically depicts an exemplary apparatus for curing a coated glass fiber in accordance with one aspect of the present invention.

FIG. 2 schematically depicts a cross-sectional view of an elliptic cylinder having a reflective inner surface.

FIG. 3 schematically depicts a perspective view of an exemplary apparatus for curing a coated glass fiber.

FIG. 4 schematically depicts a cross-sectional view of an exemplary apparatus for curing a coated glass fiber.

FIG. 5 schematically depicts a cross-sectional view of another exemplary apparatus for curing a coated glass fiber.

FIG. 6 depicts a cross-sectional view of an exemplary apparatus for curing a coated glass fiber in accordance with another aspect of the present invention.

FIG. 7 a schematically depicts the emission pattern of a UVLED having an emission pattern of cos^(1.5)(Φ).

FIG. 7 b schematically depicts the emission pattern of a UVLED having an emission pattern of cos²(Φ).

DETAILED DESCRIPTION

The present invention embraces an apparatus, a system, and a method for curing glass-fiber coatings (e.g., primary coatings, secondary coatings, and/or tertiary ink layers).

The apparatus employs a plurality of UV-radiation sources (e.g., UVLEDs) that are configured to emit UV radiation toward a drawn glass fiber to cure its coating(s) (e.g., primary coatings, secondary coatings, and/or tertiary ink layers). The UV-radiation sources are typically positioned within a cavity (e.g., a substantially cylindrical cavity) that defines a curing axis along which an optical fiber (i.e., a glass fiber having one or more coating layers) may pass during the curing process. FIG. 1 schematically depicts an exemplary apparatus 10 that includes a plurality of UV-radiation sources 11 directing UV radiation toward a curing axis 12.

The apparatus for curing coated glass fibers has a plurality of UV-radiation sources that emit electromagnetic radiation having wavelengths of between about 200 nanometers and 600 nanometers. By way of example, the UV-radiation sources may emit electromagnetic radiation having wavelengths of between about 200 nanometers and 450 nanometers (e.g., between about 250 nanometers and 400 nanometers). In a particular exemplary embodiment, a UV-radiation source may emit electromagnetic radiation having wavelengths of greater than about 300 nanometers (e.g., between about 300 nanometers and 400 nanometers). In another particular exemplary embodiment, a UV-radiation source may emit electromagnetic radiation having wavelengths of between about 350 nanometers and 425 nanometers.

Typically, an apparatus in accordance with the present invention employs respective UV-radiation sources that emit differing bands of UV radiation (e.g., one UV-radiation source that mostly emits at wavelengths of between about 200 nanometers and 300 nanometers and another UV-radiation source that mostly emits at wavelengths greater than 300 nanometers).

The UV-radiation sources (e.g., UVLEDs) usually emit UV radiation within a relatively narrow band (e.g., varying by no more than about 30 nanometers). More typically, the UV-radiation sources emit UV radiation within a band that varies by no more than about 20 nanometers (e.g., varying by no more than about 10 nanometers). Typically, UVLEDs are employed as UV-radiation sources because UVLEDs are capable of emitting wavelengths within a much smaller spectrum than conventional UV lamps (e.g., mercury lamps and/or fusion lamps), thereby promoting more efficient curing. UV lasers (e.g., excimer lasers and semiconductor lasers) may also be employed as UV-radiation sources. That said, the apparatus disclosed herein may be modified to employ mercury lamps and/or fusion lamps as radiation sources (e.g., as a supplemental source of UV radiation).

In this regard, although an exemplary UV-radiation source emits substantially all of its electromagnetic radiation within a defined range (e.g., between 350 nanometers and 450 nanometers, such as between 370 nanometers and 400 nanometers), the UV-radiation source may emit small amounts of electromagnetic radiation outside the defined range. In this regard, 80 percent or more (e.g., at least about 90 percent) of the output (i.e., emitted electromagnetic radiation) of an exemplary UV-radiation source is typically emitted within a narrowly defined range (e.g., between about 375 nanometers and 425 nanometers). For example, at least about 80 percent (e.g., 85-95 percent) of the electromagnetic radiation emitted by a UV-radiation source might have wavelengths within a 15-nanometer range (e.g., within a 10-nanometer range).

In one embodiment, the apparatus includes one or more sources of UV radiation that emit UV radiation mostly having wavelengths of between about 200 nanometers and 300 nanometers (e.g., between about 230 nanometers and 270 nanometers). In a particular embodiment, some of the UV-radiation sources emit UV radiation mostly having wavelengths of between about 245 nanometers and 265 nanometers, such as between about 250 nanometers and 260 nanometers (e.g., about 254 nanometers).

Such UV-radiation sources (e.g., UV-radiation sources emitting wavelengths mostly between about 220 nanometers and 280 nanometers) emit UV radiation at wavelengths well below the absorbance peaks of typical photoinitiators (e.g., acyl phosphine oxides and/or benzophenones) that are present in exemplary UV-curable coatings. In other words, the coating or coatings being cured typically do not have an absorption peak between about 200 nanometers and 300 nanometers (e.g., no absorption peak at less than 350 nanometers). Surprisingly, it has now been discovered that shorter wavelengths are useful for focusing UV radiation at the surface of the coating. Focusing UV radiation at the surface of the coating creates a relatively high concentration of free radicals there (i.e., at the coating surface). The high concentration of free radicals quickly consumes oxygen near the surface of the coating. Thereafter, oxygen no longer interferes with the polymerization of the coating.

The apparatus also typically includes one or more UV-radiation sources that emit UV radiation corresponding to one or more absorption peaks of the photoinitiators in the glass-fiber coating. Those having ordinary skill will appreciate that glass fiber may have more than one coating layer (e.g., a primary coating and secondary coating), which may have different absorption peaks.

Typically, the apparatus employs UV-radiation sources that have a mean output wavelength within about 15 nanometers, more typically within about 10 nanometers (e.g., within about 5 nanometers) of a targeted absorption peak. That said, it is within the scope of the present invention to employ UV-radiation sources that have a mean output wavelength (i) at least about 15 nanometers less than a targeted absorption peak or (ii) at least about 15 nanometers greater than a targeted absorption peak (e.g., at least about 20 nanometers greater than a targeted absorption peak).

Moreover, to promote efficient polymerization, a substantial portion (e.g., at least about 80 percent) of a source's emitted UV radiation is typically within about 10 nanometers (e.g., +/−5 nanometers) of a UV-radiation source's mean output.

Typically, the absorption peaks for the glass-fiber-coating photoinitiators occur at wavelengths greater than 300 nanometers (e.g., between about 350 nanometers and 450 nanometers). By way of example, an exemplary glass-fiber coating has photoinitiators (e.g., bis-acylphosphine oxide) with absorption peaks at about 370 nanometers, 385 nanometers, and 400 nanometers. Typically, the absorption peaks are separated by at least 10 nanometers (e.g., 15-25 nanometers).

Accordingly, the apparatus may include one or more UV-radiation sources emitting UV radiation at wavelengths of between about 360 nanometers and 380 nanometers (e.g., between about 365 nanometers and 375 nanometers). The apparatus may also include one or more UV-radiation sources emitting UV radiation at wavelengths of between about 375 nanometers and 395 nanometers (e.g., between about 380 nanometers and 390 nanometers) and one or more UV-radiation sources emitting UV radiation at wavelengths of between about 390 nanometers and 410 nanometers (e.g., between about 395 nanometers and 405 nanometers).

In a typical arrangement, the lower wavelength UV-radiation sources (e.g., emitting wavelengths between about 230 nanometers and 270 nanometers) are positioned within the apparatus so that a coated glass fiber is exposed to the lower-wavelength UV radiation before being exposed to UV radiation corresponding to one or more absorption peaks. Alternatively, a coated glass fiber may be concurrently exposed to lower-wavelength UV radiation and to UV radiation corresponding to one or more absorption peaks. That said, it is within the scope of the invention to otherwise vary the timing of the respective UV-radiation exposures.

As depicted in FIG. 1, a protective tube 13 typically surrounds the curing axis 12. By way of example, a transparent quartz tube (e.g., a quartz tube that is substantially transparent to UV radiation emitted by the UV-radiation sources) having an outer diameter of about 24 millimeters and a thickness of about 2 millimeters may be employed as a protective tube. In another embodiment, the protective tube (e.g., a transparent quartz tube) may have an outer diameter of between about 3 millimeters and 12 millimeters (e.g., about 10 millimeters) and a thickness of about 1 millimeter. In yet another embodiment, the protective tube has a substantially transparent outer surface, but a reflective or semi-reflective inner surface.

The protective tube prevents curing byproducts from damaging and/or fouling the UV-radiation sources within the cavity. In this regard, volatile components of the optical-fiber coating have a tendency to evaporate during curing. In the absence of a protective tube, these curing byproducts can precipitate onto both the UV-radiation sources and the cavity's inner surface. The protective tube can also prevent uncured coating (e.g., delivered by a coating applicator) from being inadvertently deposited within the cavity (e.g., spilled onto the UV-radiation sources and/or the cavity's inner surface).

An inert gas (e.g., nitrogen) or gas mixture (e.g., nitrogen and oxygen) may be introduced into the protective tube to provide an oxygen-free or a reduced-oxygen environment around an optical fiber as its coating is being cured. In this regard, it has been observed that having a small amount of oxygen may promote efficient curing. Accordingly, the protective tube may provide an environment having between about 0.1 percent and 5 percent oxygen, such as between about 0.2 percent and 3 percent oxygen (e.g., about 0.31 percent oxygen). Providing a reduced-oxygen environment around the coated glass fiber seems to help reduce the consumption of free radicals by the oxygen.

In a particular embodiment, one or more pipes (e.g., pipes 15 a and 15 b depicted in FIG. 1) provide a controlled flow of gas into the protective tube 13. A seal 14 is typically positioned at the top of the protective tube 13 to prevent the ingress of gas into the protective tube 13 (as well as the egress of gas from the protective tube). The environment within the protective tube may be kept at a higher pressure than the external environment to further preclude the ingress of unwanted gases into the protective tube. Typically, a probe is positioned within the protective tube. If this probe detects an undesirable amount of oxygen within the protective tube, the amount of gas (e.g., oxygen and nitrogen) flowing into the protective tube can be adjusted.

In one embodiment, an annular plate having a number of small holes is positioned at the top of the protective tube. When gas (e.g., nitrogen and oxygen) is blown into the protective tube, the annular plate creates a layer of gas that helps to keep undesirable amounts of oxygen out of the protective tube.

Furthermore, the gas (e.g., nitrogen and/or oxygen) flowing through the protective tube may be heated, such as by employing one or more heat rings positioned around (i) the protective tube and/or (ii) a pipe supplying gas to the protective tube. FIG. 1 depicts heat rings 16 being positioned around the protective tube 13 to create a heated environment. Alternatively, the gas flowing through the protective tube may be heated using infrared heaters. Accordingly, the gas within the protective tube typically is maintained at a temperature between about 25° C. and 150° C. The protective tube may include a probe for detecting the temperature within the protective tube, thereby allowing for temperature adjustments. Heating the gas flow helps to remove unreacted coating components (e.g., coating monomers) and/or unwanted byproducts present in the cured coating.

In a particular embodiment, the apparatus for curing glass-fiber coatings includes a UVLED source, such as one or more ultraviolet light emitting diodes (UVLEDs), positioned within a cylindrical cavity (or a substantially cylindrical cavity) that has a reflective inner surface. To achieve the reflective inner surface, the cylindrical cavity may be made from stainless steel or metalized glass, such as silvered quartz, or other suitable material (e.g., a mirror with a polished metallic surface). In addition, the interior of the cylindrical cavity defines a curing space. In turn, the curing space defines a curing axis along which a drawn glass fiber passes during the curing process. As noted, a protective tube typically surrounds the curing axis. Optical models have demonstrated that employing a smaller protective tube generally improves curing efficiency (i.e., reduce UV radiation waste).

In a typical embodiment, the cylindrical cavity has an elliptical cross-section. In other words, the cylindrical cavity usually has the shape of an elliptic cylinder. By way of illustration, an exemplary elliptic cylinder has a major axis length of 54 millimeters and a minor axis length of 45.8 millimeters. For an elliptic cylinder, the curing axis corresponds with one of the two line foci defined by the elliptic cylinder. Moreover, it is thought that the cylinder's elliptical shape can be modified to compensate for the deleterious effects that may be caused by the protective tube (e.g., refraction and reflection).

In an alternative embodiment, the cylindrical cavity has a circular cross-section, such as a cylindrical cavity with a diameter of less than 50 millimeters (e.g., a diameter of 20 millimeters or less, such as about 10 millimeters).

It will be appreciated by those having ordinary skill in the art that a UVLED does not emit UV radiation only toward a point or line, but rather emits UV radiation in many directions. Thus, most of the UV radiation emitted by a UVLED will not directly strike a glass-fiber coating to effect curing. In curing an optical-fiber coating, however, it is desirable that as much UV radiation as possible strike the optical fiber (i.e., a coated glass fiber).

Accordingly, the reflective surface of the cylindrical cavity can reflect otherwise misdirected UV radiation onto an optical fiber for curing, thus reducing wasted energy. Moreover, for a cylindrical cavity having an elliptical cross-section, any electromagnetic radiation that is emitted from one line focus (regardless of direction) will be directed toward the other line focus after being reflected at the inner surface of the cylinder. This principle is illustrated in FIG. 2, which schematically depicts a cross-sectional view of a reflective elliptic cylinder 17 having a first line focus 18 a and a second line focus 18 b. As depicted in FIG. 2, each UV ray 19 emitted from the first line focus 18 a will intersect the second line focus 18 b.

Accordingly, in one embodiment, each UVLED source may be positioned along the other line focus (i.e., the line focus that does not correspond with a curing axis) such that each UVLED source emits UV radiation in the general direction of the curing axis. In this regard, FIGS. 3 and 4 depict an exemplary apparatus 20 for curing a coated glass fiber 26. The apparatus 20 includes a substantially cylindrical cavity 25 having an elliptical shape and a reflective inner surface. The cavity 25 defines a first line focus 21 and a second line focus 22. One or more UVLED sources 24 are positioned along the first line focus 21. Typically, each UVLED source 24 is formed from a single light emitting diode. That said, it is within the scope of the present invention to employ an array of small light emitting diodes to form each UVLED source 24.

In one embodiment, the apparatus 20 may include a plurality of UVLED sources 24 positioned contiguously to one another along the first line focus 21 (i.e., directly stacked). In another embodiment, adjacent UVLED sources may be vertically separated by a space of at least about 5 millimeters (e.g., at least about 10 millimeters). The second line focus 22 further defines a curing axis along which a coated glass fiber 26 passes so it can be cured. As depicted in FIG. 4, UV rays 23 emitted from the UVLED source 24 may reflect off the inner surface of the cavity 25 such that the reflected UV rays 23 are incident to the coated glass fiber 26.

To facilitate uniform curing of the coated glass fiber 26, some of the UVLED sources 24 may be differently oriented. The apparatus 20 typically includes a single UVLED positioned within a particular horizontal plane. In an alternative embodiment, multiple UVLEDs may be positioned (e.g., at a point other than the first focal line) within a horizontal plane to promote more uniform curing of the glass fiber.

In another embodiment, a system for curing a coated glass fiber may include a plurality of differently oriented cavity segments (e.g., apparatuses for curing a coated glass fiber). Each cavity may have a common curing axis (e.g., the second focal line), but a different first line focus.

As depicted in FIG. 3, a second apparatus 30 for curing a glass fiber may have a different orientation than the first apparatus 20 (e.g., the second apparatus 30 may have UVLED sources positioned along a line focus 31 that differs from the first line focus 21). As further illustrated in FIG. 3, the second apparatus 30 is rotated 180 degrees relative to the orientation of the first apparatus 20. That said, various degrees of rotation may separate adjacent cavity segments (i.e., adjacent apparatuses). By way of non-limiting illustration, a 45-degree rotation, a 90-degree rotation, or a 135-degree rotation may separate adjacent cavity segments while maintaining the common curing axis.

In this regard, the positioning of a plurality of cavity segments in a three-dimensional arrangement may be defined by the cylindrical coordinate system (i.e., r, θ, z). Using the cylindrical coordinate system and as described herein, the curing axis defines a z-axis. Furthermore, as herein described and as will be understood by those having ordinary skill in the art, the variable r is the perpendicular distance of a point to the z-axis. The variable θ describes the angle in a plane that is perpendicular to the z-axis. In other words and by reference to a Cartesian coordinate system (i.e., defining an x-axis, a y-axis, and a z-axis), the variable θ describes the angle between a reference axis (e.g., the x-axis) and the orthogonal projection of a point onto the x-y plane. Finally, the z variable describes the height or position of a reference point along the z-axis.

Thus, a point is defined by its cylindrical coordinates (r, θ, z). For cavity segments employed in exemplary configurations, the variable r is usually constant and may refer to the distance between the first line focus of a cavity segment and the curing axis (e.g., where the respective cavity segments employ the same elliptical dimensions). Accordingly, to the extent the variable r is largely fixed, the position of the cavity segments can be described by their respective z and θ coordinates.

By way of non-limiting example, a plurality of cavity segments having the same elliptical dimensions may be positioned in a helical arrangement with the first cavity segment at the position (1, 0, 0), where r is fixed at a constant distance (i.e., represented here as a unitless 1). Additional cavity segments may be positioned, for example, every 90 degrees (i.e., π/2) with a Δz of 1 (i.e., a positional step change represented here as a unitless 1). Thus, a second cavity segment would have the coordinates (1, π/2, 1), a third cavity segment would have the coordinates (1, π, 2), and a fourth cavity segment would have the coordinates (1, 3π/2, 3), thereby defining a helical configuration. In other words, the respective cavity segments are rotated around the curing axis.

That said, the respective distances r and z need not be equivalent. Moreover, the several cavity segments in an arrangement as herein disclosed need not be offset by 90 degrees (e.g., π/2, π, 3π/2, etc.). For example, the respective cavity segments may be offset by 60 degrees (e.g., π/3, 2π/3, π, etc.) or by 120 degrees (e.g., 2π/3, 4π/3, 2π, etc.). Indeed, the cavity segments in an arrangement as discussed herein need not follow a regularized helical rotation.

Commonly assigned U.S. Patent Application Nos. 61/346,806 and 61/351,151 filed May 20, 2010, and Jun. 3, 2010, respectively, for a Curing Apparatus Employing Angled UVLEDs, (Molin), each of which is hereby incorporated by reference in its entirety, disclose that a protective tube may interfere with UV radiation directed toward a curing axis. Accordingly, an apparatus for curing a coated glass fiber may employ one or more angled UVLEDs (i.e., UVLEDS having an emission angle of greater than 0 degree relative to the coated glass fiber).

In this regard, the optimum emission angle is typically at least about 30 degrees, such as between 30 degrees and 100 degrees (e.g., about 90 degrees for a UVLED having a width of about 0.3 millimeter or less), more typically between about 30 degrees and 60 degrees (e.g., about 45 degrees for a UVLED having a width of about 0.22 millimeter), between each UVLED source and the major axis of the elliptical cylinder. In this regard, ever smaller UVLEDs may facilitate the deployment of a curing apparatus that can efficiently employ emission angles approaching 180 degrees. By way of example, such a curing apparatus might employ emission angles greater than about 100 degrees, such as between about 120 degrees and 150 degrees (e.g., about 135 degrees). When a protective tube is present within the elliptical cylinder (i.e., surrounding the curing axis), employing an angled UVLED source in this way will provide improved UV absorption during curing.

Accordingly, FIG. 5 depicts another exemplary apparatus 50 for curing a coated glass fiber 26 in accordance with the present invention. In particular, the apparatus 50 employs one or more angled UVLED sources 24 positioned within a substantially cylindrical cavity 25 having an elliptical shape and a reflective inner surface. The cavity 25 defines a first line focus 21 and a second line focus 22. The second line focus 22 defines a curing axis. A coated glass fiber 26 passes along the curing axis during curing. Finally, a protective tube 35 surrounds the curing axis and the coated glass fiber 26.

The cavity 25 also defines a major axis 34 that intersects the first line focus 21 and the second line focus 22. One or more UVLED sources 24 are positioned along the first line focus 21. Each UVLED source 24 emits UV rays 23 in a distinctive emission pattern. In general, an emission pattern has a line of average emission L_(avg) 23 a (i.e., an average of all the UV rays emitted by the UVLED source 24).

In an exemplary embodiment, an UVLED source 24 is angled away from the coated glass fiber 26. In particular, the UVLED source 24 is positioned so that an emission angle α is defined between the line of average emission L_(avg) 23 a and the elliptical cylinder's major axis 34. The emission angle α is typically between about 30 degrees and 100 degrees (e.g., between 30 degrees and 60 degrees), more typically between about 40 degrees and 50 degrees (e.g., 45 degrees).

Although the emission angle α is typically calculated relative to the line of average emission L_(avg) for a UVLED source (e.g., a single UVLED), it is within the scope of the invention to describe the emission angle α relative to a line defined by a UVLED source's median or mode (i.e., a line of maximum emission L_(max)).

Typically, each UVLED source within the cavity is oriented to have the same emission angle. That said, it is within the scope of the present invention to orient UVLED sources within the cavity such that the UVLED sources have different emission angles.

Those having ordinary skill in the art will appreciate that the UV radiation emitted from a UVLED is not emitted from a single point. Therefore, and because of the small size of a coated glass fiber (e.g., a 250-micron diameter), it is desirable to use small UVLED sources (e.g., a 3-millimeter square UVLED or a 1-millimeter square UVLED). In general, a greater percentage of reflected UV radiation will be incident to the coated glass fiber using a small UVLED as compared with using a larger UVLED.

Moreover, each UVLED source may include a lens (e.g., a convex lens, such as a biconvex or plano-convex lens) for focusing emitted UV radiation. In particular, each lens may have a focus at one of the two line foci (e.g., the line focus not defining a curing axis). For example, a cylindrical lens with a high numerical aperture can be used to rescale a 3-millimeter square UVLED, so that it has an effective width of about 0.4 millimeter or less at the line focus. By including a lens with each UVLED, the efficiency of the apparatus may be further enhanced.

In an alternative embodiment, the apparatus for curing a coated glass fiber may employ one or more optical fibers (e.g., one or more multimode optical fibers) to transmit UV radiation. In this regard, these optical fibers are typically positioned along the first line focus of the apparatus as an alternative to positioning UVLEDs along the first line focus. Alternatively, one or more of these optical fibers may be positioned within an apparatus for curing a coated glass fiber in a manner similar to that disclosed herein with respect to UV-radiation sources.

Typically, each optical fiber is coupled to one or more sources of UV radiation, such as a UVLED. By way of example, a plurality of small UVLEDS may be coupled to a plurality of optical fibers in a one-to-one relationship (e.g., 20 UVLEDS and 20 optical fibers). Thereupon, the optical fibers may be configured in various arrays at or near the first line focus.

Moreover, at least one—and typically each—optical fiber is oriented at the first line focus to provide an emission angle of between about 30 degrees and 120 degrees (e.g., between 45 degrees and 90 degrees). Such optical fibers typically employ a central glass fiber, but may alternatively employ a central plastic fiber.

Moreover, the use of an optical fiber to transmit UV radiation into the cavity may facilitate the deployment of a curing apparatus that can efficiently employ emission angles approaching 180 degrees. By way of example, such a curing apparatus might employ emission angles between 120 degrees and 180 degrees (e.g., about 150 degrees).

To simplify coupling with the UVLED source(s), multimode optical fibers are typically employed for purposes of UV-radiation transmission. That said, it is within the scope of the present invention to employ single-mode optical fibers (e.g., holey glass fibers). An exemplary single-mode optical fiber is a large-mode-area fiber (LMA) that provides a Gaussian beam having a diameter of 0.1 millimeter or less. An exemplary holey optical fiber is disclosed in commonly assigned U.S. Patent Application Publication No. 2010/0189397 for a Single-Mode Optical Fiber, (Richard et al.), which is hereby incorporated by reference in its entirety.

To supplement the foregoing disclosure, this application incorporates entirely herein by reference commonly assigned U.S. Patent Application Publication No. US2010/0183821 A1 for a UVLED Apparatus for Curing Glass-Fiber Coatings (Hartsuiker et al.); commonly assigned U.S. patent application Ser. No. 13/111,147 for a Curing Apparatus Employing Angled UVLEDs, filed May 19, 2011, (Molin); commonly assigned U.S. Patent Application No. 61/346,806 for a Curing Apparatus Employing Angled UVLEDs, filed May 20, 2010, (Molin); commonly assigned U.S. Patent Application No. 61/351,151 for a Curing Apparatus Employing Angled UVLEDs, filed Jun. 3, 2010, (Molin); and commonly assigned U.S. Patent Application No. 61/372,312 for a Method and Apparatus Providing Increased UVLED Intensity, filed Aug. 10, 2010, (Overton). This application further incorporates entirely herein by reference U.S. Pat. No. 4,683,525; U.S. Pat. No. 4,710,638; U.S. Pat. No. 7,022,382; U.S. Pat. No. 7,173,266; U.S. Pat. No. 7,399,982; U.S. Pat. No. 7,498,065; and U.S. Patent Application Publication No. 2003/0026919.

In yet another particular embodiment, an apparatus for curing a coated glass fiber may employ a plurality of UV-radiation sources within a horizontal plane.

FIG. 6 depicts a cross-sectional view of an exemplary apparatus 60. Typically, the apparatus 60 includes a plurality of UV-radiation sources 61 emitting within a first wavelength range corresponding to an absorption peak of the photoinitiators within a glass-fiber coating. Moreover, the apparatus typically includes a plurality of UV-radiation sources 62 and 63 (e.g., UVLEDs) emitting within a second wavelength range and a third wavelength range, respectively. The second and third wavelength ranges typically correspond to respective absorption peaks of the photoinitiators within a glass-fiber coating. Alternatively, one or more of the UV-radiation sources may emit UV radiation below the absorption peaks of the photoinitiators within a glass-fiber coating.

The apparatus 60 defines a curing axis 64 along which a coated glass fiber may pass. As depicted in FIG. 6, the apparatus 60 typically defines a cylindrical cavity 65 having a circular cross section. Accordingly, the line focus of the cylindrical cavity 65 typically defines the curing axis 64. That said, in alternative embodiments the cylindrical cavity may define an elliptical or half-circular cross section.

Typically, the UV-radiation sources are circumferentially positioned around the curing axis. Furthermore, the UV-radiation sources are positioned around the coated glass fiber so as to focus UV radiation on the coated glass fiber.

As noted, UV-radiation sources (e.g., UVLEDs) can have various emission patterns (e.g., far field pattern). By way of example, a UVLED employed in accordance with the present invention may have a substantially Lambertian emission pattern. In other embodiments, a UV-radiation source (e.g., a UVLED) may have a Gaussian or multimodal emission pattern. Another exemplary UVLED may have an emission pattern of cos^(1.5)(Φ) or cos²(Φ). FIG. 7 a schematically depicts the emission pattern of a UVLED having an emission pattern of cos^(1.5)(Φ). FIG. 7 b schematically depicts the emission pattern of a UVLED having an emission pattern of cos²(Φ).

UVLEDs are typically much smaller than conventional UV lamps (e.g., mercury bulbs). By way of example, a UVLED may be a 0.25-inch square UVLED. The UVLED may be affixed to a platform (e.g., a 1-inch square or larger mounting plate). Of course, other UVLED shapes and sizes are within the scope of the present invention. By way of example, a 3-millimeter square UVLED may be employed in the apparatus according to the present invention.

Each UVLED may have a power output of as much as 32 watts (e.g., a UVLED having a power input of about 160 watts and a power output of about 32 watts). That said, UVLEDs having outputs greater than 32 watts (e.g., 64 watts) may be employed as such technology becomes available. Using UVLEDs with higher power output may be useful for increasing the rate at which optical-fiber coatings cure, thus promoting increased production line speeds. Alternatively, UVLEDs having lower power outputs (e.g., around 8 watts) may be employed, though the minimum power output for UVLEDs is usually about 4 watts.

Alternatively, the output of a UVLED may be described in terms of irradiance. Accordingly, each UVLED source typically has an irradiance of at least about 2 w/cm², more typically at least about 4 w/cm² (e.g., at least about 8 w/cm²).

Each UVLED source may be positioned at a distance of between about 1 millimeter and 100 millimeters (e.g., typically between about 5 millimeters and 30 millimeters) from the optical fiber to be cured (e.g., from the curing axis). More typically, each UVLED source is positioned at a distance of about 25 millimeters from the optical fiber to be cured. Alternatively, each UVLED source may be positioned closer at a distance of between about 2 millimeters and 10 millimeters (e.g., about 5 millimeters) from the optical fiber to be cured.

It will be further appreciated by those having ordinary skill in the art that UV-radiation sources may absorb incident electromagnetic radiation, which might diminish the quantity of reflected UV radiation available for absorption by the glass-fiber coating. Moreover, incident UV radiation can damage a UV-radiation source. Therefore, in an apparatus for curing glass-fiber coatings that has a plurality of UV-radiation sources, it may be desirable to position the UV-radiation sources in a way that reduces UV radiation incident to the UV-radiation sources. Accordingly, a vertical space of at least about 10 millimeters may separate adjacent UV-radiation sources. Moreover, the UV-radiation sources may employ a reflective surface (e.g., a surface coating) that promotes reflection of incident electromagnetic radiation yet permits the transmission of emitted electromagnetic radiation.

It may be desirable for the power of the UV radiation incident to the optical fiber to vary as the optical fiber progresses through the apparatus. Varying the power of the UV radiation may enhance the curing of the glass-fiber coating. Depending on the curing properties of a particular coating, it may be desirable to initially expose the optical fiber to high intensity UV radiation. Alternatively, it may be desirable to initially expose the optical fiber to lower intensity UV radiation (e.g., between about 10 percent and 50 percent of the maximum exposure intensity) before exposing the optical fiber to high intensity UV radiation (e.g., the maximum intensity to which the optical fiber is exposed). In this regard, initially exposing the optical fiber to lower intensity UV radiation may be useful in controlling the generation of free radicals in an uncured coating. Those having ordinary skill in the art will appreciate that if too many free radicals are present, many of the free radicals may recombine rather than encourage the polymerization of the glass-fiber coating—an undesirable effect. Accordingly, in an apparatus containing a plurality of UV-radiation sources, the intensity of the UV radiation output from the UV-radiation sources may vary.

In this regard, an apparatus as described herein may include a dark space between one or more UV-radiation sources. In other words, the apparatus may include a space in which substantially no UV radiation is incident to the optical fiber being cured. A pause in the curing process provided by a dark space can help to ensure even and efficient curing of the optical-fiber coatings. In particular, a dark space may be useful in preventing too many free radicals from being present in a glass-fiber coating before it is cured (i.e., dark space helps to control free-radical generation).

For example, it may be desirable to initially expose an optical fiber to low power UV radiation and then pass the optical fiber through a dark space. After the optical fiber passes through a dark space, it is exposed to higher power UV radiation to complete the curing process. A curing apparatus employing dark space is disclosed in commonly assigned U.S. Pat. No. 7,322,122 for a Method and Apparatus for Curing a Fiber Having at Least Two Fiber Coating Curing Stages, which is hereby incorporated by reference in its entirety.

Moreover, an apparatus for curing glass-fiber coatings may include a control circuit for controlling the UV radiation output from the UV-radiation sources. The control circuit may be used to vary the intensity of the UV radiation as an optical fiber progresses through the apparatus.

Alternatively, to ensure that the optical fiber receives a consistent dose of ultraviolet radiation, the UV radiation output of the UV-radiation sources may vary with the speed at which the optical fiber passes through the apparatus. That is to say, at higher speeds (i.e., the speed the optical fiber passes through the apparatus), the output intensity of the UV-radiation sources may be greater than the output intensity at lower speeds. The output intensity of the UVLED sources may be controlled by reducing (or increasing) the current flowing to the UV-radiation sources.

Finally, the glass fiber is typically rotated or otherwise subjected to perturbations during drawing operations to reduce unwanted dispersion effects. It is thought that this may further enhance the curing process as herein described.

In accordance with the foregoing, the present invention embraces a method for curing a coating on a glass fiber.

In an exemplary embodiment, the method includes applying a coating to a glass fiber and then passing the coated glass fiber through a cavity (e.g., along the cavity's curing axis). As noted, the glass fiber typically does not have a coating having an absorption peak that is between about 200 nanometers and 300 nanometers but does have a coating having one or more absorption peaks occurring at wavelength(s) greater than about 300 nanometers (e.g., greater than 325 nanometers, such as about 370 nanometers). In some instances, the glass fiber does not have a coating having an absorption peak of less than about 350 nanometers.

UV radiation is directed from a first UV-radiation source to promote the curing of the coating (i.e., the coating is exposed to the UV radiation). Typically, at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 200 nanometers and 300 nanometers (e.g., between about 230 nanometers and 270 nanometers).

UV radiation is also directed from a second UV-radiation source to promote the curing of the coating. Typically, at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths within 10 nanometers of the coating's first absorption peak (e.g., most of the electromagnetic radiation might be emitted between 360-380 nanometers, 375-395 nanometers, or 390-410 nanometers).

For a coating having a second absorption peak occurring at a wavelength greater than 300 nanometers, UV radiation may be directed from a third UV-radiation source to promote the curing of the coating. In this regard, typically at least about 80 percent of the electromagnetic radiation emitted by the third UV-radiation source has wavelengths within 10 nanometers of the coating's second absorption peak.

In a particular process embodiment, (i) at least about 80 percent (e.g., 90 percent) of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 220 nanometers and 280 nanometers (e.g., 245 nanometers and 265 nanometers), (ii) at least about 80 percent (e.g., 90 percent) of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths of more than 350 nanometers (e.g., between about 360 nanometers and 380 nanometers), and (iii) at least about 80 percent (e.g., 90 percent) of the electromagnetic radiation emitted by the third UV-radiation source has wavelengths of more than 375 nanometers (e.g., between about 390 nanometers and 410 nanometers).

The foregoing description embraces the curing of one or more coating layers on a glass fiber. The disclosed apparatus, system, and method may be similarly employed to cure a buffer layer onto an optical fiber or a ribbon matrix around a plurality of optical fibers.

Relative to other UV-radiation sources, UVLED devices typically generate a smaller amount of heat energy. That said, to dissipate the heat energy created by a UVLED, a heat sink may be attached to the UVLED (or otherwise positioned to cool the UVLED head). For example, the heat sink may be located behind the UVLED (e.g., opposite the portion of the UVLED that emits UV radiation). Alternatively, the heat sink may be located above or below the UVLED. The heat sink may be one-inch square, although other heat sink shapes and sizes are within the scope of the present invention.

The heat sink may be formed of a material suitable for conducting heat (e.g., brass, aluminum, stainless steel, or copper). The heat sink may include a heat exchanger that employs a liquid coolant (e.g., chilled water), which circulates within the heat exchanger to draw heat from the UVLED. In another embodiment, the heat sink may include a heat exchanger that employs a gas coolant (e.g., nitrogen, helium, or argon).

Removing heat generated by the UVLED is important for several reasons. First, excess heat may slow the rate at which optical-fiber coatings cure. Furthermore, excess heat can cause the temperature of the UVLED to rise, which can reduce UV-radiation output. Indeed, continuous high-temperature exposure can permanently reduce the UVLED's radiation output and/or the UVLED's lifespan. With adequate heat removal, however, the UVLED may have a useful life of 7,000 hours or more (e.g., 50,000 hours).

In accordance with the foregoing, the resulting optical fiber includes one or more coating layers (e.g., a primary coating and a secondary coating). At least one of the coating layers—typically the secondary coating—may be colored and/or possess other markings to help identify individual fibers. Alternatively, a tertiary ink layer may surround the primary and secondary coatings.

For example, the resulting optical fiber may have one or more coatings (e.g., the primary coating) that include a UV-curable, urethane acrylate composition. In this regard, the primary coating may include between about 40 and 80 weight percent of polyether-urethane acrylate oligomer as well as photoinitiator, such as LUCIRIN® TPO, which is commercially available from BASF. In addition, the primary coating typically includes one or more oligomers and one or more monomer diluents (e.g., isobornyl acrylate), which may be included, for instance, to reduce viscosity and thereby promote processing. Exemplary compositions for the primary coating include UV-curable urethane acrylate products provided by DSM Desotech (Elgin, Ill.) under various trade names, such as DeSolite® DP 1011, DeSolite® DP 1013, DeSolite® DP 1014, DeSolite® DP 1014XS, and DeSolite® DP 1016. An exemplary coating system is available from Draka Comteq under the trade name ColorLock® ^(XS).

Those having ordinary skill in the art will recognize that an optical fiber with a primary coating (and an optional secondary coating and/or ink layer) typically has an outer diameter of between about 235 microns and about 265 microns (μm). The component glass fiber itself (i.e., the glass core and surrounding cladding layers) typically has a diameter of about 125 microns, such that the total coating thickness is typically between about 55 microns and 70 microns.

In another alternative embodiment, the outer diameter of the component glass fiber may be reduced to less than 125 microns (e.g., between about 60 microns and 120 microns), perhaps between about 70 microns and 115 microns (e.g., about 80-110 microns). This may be achieved, for instance, by reducing the thickness of one or more cladding layers.

As compared with the prior alternative embodiment, (i) the total diameter of the optical fiber may be reduced (i.e., the thickness of the primary and secondary coatings are maintained in accordance with the prior alternative embodiment) or (ii) the respective thicknesses of the primary and/or secondary coatings may be increased relative to the prior alternative embodiment (e.g., such that the total diameter of the optical fiber might be maintained).

By way of illustration, with respect to the former, a component glass fiber having a diameter of between about 90 and 100 microns might be combined with a primary coating layer having an outer diameter of between about 110 microns and 150 microns (e.g., about 125 microns) and a secondary coating layer having an outer diameter of between about 130 microns and 190 microns (e.g., about 155 microns). With respect to the latter, a component glass fiber having a diameter of between about 90 and 100 microns might be combined with a primary coating layer having an outer diameter of between about 120 microns and 140 microns (e.g., about 130 microns) and a secondary coating layer having an outer diameter of between about 160 microns and 230 microns (e.g., about 195-200 microns).

It seems that reducing the diameter of the component glass fiber might make the resulting optical fiber more susceptible to microbending attenuation. For example, as compared with a component glass fiber having a standard diameter of 125 microns, a component glass fiber having a diameter of 110 microns might be twice as susceptible to microbending losses. That said, the advantages of further reducing optical-fiber diameter may be worthwhile for some optical-fiber applications.

As noted, the component glass fiber typically has an outer diameter of about 125 microns. With respect to the optical fiber's surrounding coating layers, the primary coating may have an outer diameter of between about 175 microns and about 195 microns (i.e., a primary coating thickness of between about 25 microns and 35 microns) and the secondary coating may have an outer diameter of between about 235 microns and about 265 microns (i.e., a secondary coating thickness of between about 20 microns and 45 microns). Optionally, the optical fiber may include an outermost ink layer, which is typically between two and ten microns thick.

In an alternative embodiment, the resulting optical fiber may possess a reduced diameter (e.g., an outermost diameter between about 150 microns and 230 microns). In this alternative optical-fiber configuration, the thickness of the primary coating and/or secondary coating is reduced, while the diameter of the component glass fiber is maintained at about 125 microns. By way of example, in such embodiments the primary coating layer may have an outer diameter of between about 135 microns and about 175 microns (e.g., about 160 microns), and the secondary coating layer may have an outer diameter of between about 150 microns and about 230 microns (e.g., more than about 165 microns, such as 190-210 microns or so). In other words, the total diameter of the optical fiber is reduced to less than about 230 microns (e.g., about 200 microns).

Exemplary coating formulations for use with the apparatus and method described herein are disclosed in the following commonly assigned applications, each of which is incorporated by reference in its entirety: U.S. Patent Application No. 61/112,595 for a Microbend-Resistant Optical Fiber, filed Nov. 7, 2008, (Overton); International Patent Application Publication No. WO 2009/062131 A1 for a Microbend-Resistant Optical Fiber, (Overton); U.S. Patent Application Publication No. US2009/0175583 A1 for a Microbend-Resistant Optical Fiber, (Overton); and U.S. Patent Application Publication No. US20100119202 A1 for a Reduced-Diameter Optical Fiber (Overton).

Although the foregoing description embraces the curing of a coating on a glass fiber to form an optical fiber, the present invention further embraces the curing of coatings on glass fibers used for various purposes and of various sizes (e.g., glass fibers having outer diameters of between about one micron and one millimeter).

To supplement the present disclosure, this application incorporates entirely by reference the following commonly assigned patents, patent application publications, and patent applications: U.S. Pat. No. 4,838,643 for a Single Mode Bend Insensitive Fiber for Use in Fiber Optic Guidance Applications (Hodges et al.); U.S. Pat. No. 7,623,747 for a Single Mode Optical Fiber (de Montmorillon et al.); U.S. Pat. No. 7,587,111 for a Single-Mode Optical Fiber (de Montmorillon et al.); U.S. Pat. No. 7,356,234 for a Chromatic Dispersion Compensating Fiber (de Montmorillon et al.); U.S. Pat. No. 7,483,613 for a Chromatic Dispersion Compensating Fiber (Bigot-Astruc et al.); U.S. Pat. No. 7,526,177 for a Fluorine-Doped Optical Fiber (Matthijsse et al.); U.S. Pat. No. 7,555,186 for an Optical Fiber (Flammer et al.); U.S. Patent Application Publication No. US2009/0252469 A1 for a Dispersion-Shifted Optical Fiber (Sillard et al.); U.S. Patent Application Publication No. US2011/0044595 A1 for a Transmission Optical Fiber Having Large Effective Area (Sillard et al.); International Patent Application Publication No. WO 2009/062131 A1 for a Microbend-Resistant Optical Fiber, (Overton); U.S. Patent Application Publication No. US2009/0175583 A1 for a Microbend-Resistant Optical Fiber, (Overton); U.S. Patent Application Publication No. US2009/0279835 A1 for a Single-Mode Optical Fiber Having Reduced Bending Losses, filed May 6, 2009, (de Montmorillon et al.); U.S. Pat. No. 7,889,960 for a Bend-Insensitive Single-Mode Optical Fiber, (de Montmorillon et al.); U.S. Patent Application Publication No. US2010/0021170 A1 for a Wavelength Multiplexed Optical System with Multimode Optical Fibers, filed Jun. 23, 2009, (Lumineau et al.); U.S. Patent Application Publication No. US2010/0028020 A1 for a Multimode Optical Fibers, filed Jul. 7, 2009, (Gholami et al.); U.S. Patent Application Publication No. US2010/0119202 A1 for a Reduced-Diameter Optical Fiber, filed Nov. 6, 2009, (Overton); U.S. Patent Application Publication No. US2010/0142969 A1 for a Multimode Optical System, filed Nov. 6, 2009, (Gholami et al.); U.S. Patent Application Publication No. US2010/0118388 A1 for an Amplifying Optical Fiber and Method of Manufacturing, filed Nov. 12, 2009, (Pastouret et al.); U.S. Patent Application Publication No. US2010/0135627 A1 for an Amplifying Optical Fiber and Production Method, filed Dec. 2, 2009, (Pastouret et al.); U.S. Patent Application Publication No. US2010/0142033 for an Ionizing Radiation-Resistant Optical Fiber Amplifier, filed Dec. 8, 2009, (Regnier et al.); U.S. Patent Application Publication No. US2010/0150505 A1 for a Buffered Optical Fiber, filed Dec. 11, 2009, (Testu et al.); U.S. Patent Application Publication No. US2010/0171945 for a Method of Classifying a Graded-Index Multimode Optical Fiber, filed Jan. 7, 2010, (Gholami et al.); U.S. Patent Application Publication No. US2010/0189397 A1 for a Single-Mode Optical Fiber, filed Jan. 22, 2010, (Richard et al.); U.S. Patent Application Publication No. US2010/0189399 A1 for a Single-Mode Optical Fiber Having an Enlarged Effective Area, filed Jan. 27, 2010, (Sillard et al.); U.S. Patent Application Publication No. US2010/0189400 A1 for a Single-Mode Optical Fiber, filed Jan. 27, 2010, (Sillard et al.); U.S. Patent Application Publication No. US2010/0214649 A1 for an Optical Fiber Amplifier Having Nanostructures, filed Feb. 19, 2010, (Burow et al.); U.S. Patent Application Publication No. US2010/0254653 A1 for a Multimode Fiber, filed Apr. 22, 2010, (Molin et al.); U.S. Patent Application Publication No. US2010/0310218 A1 for a Large Bandwidth Multimode Optical Fiber Having a Reduced Cladding Effect, filed Jun. 4, 2010, (Molin et al.); U.S. Patent Application Publication No. US2011/0058781 A1 for a Multimode Optical Fiber Having Improved Bending Losses, filed Sep. 9, 2010, (Molin et al.); U.S. Patent Application Publication No. US2011/0064367 A1 for a Multimode Optical Fiber, filed Sep. 17, 2010, (Molin et al.); U.S. Patent Application Publication No. US2011/0069724 A1 for an Optical Fiber for Sum-Frequency Generation, filed Sep. 22, 2010, (Richard et al.); U.S. patent application Ser. No. 12/944,422 for a Rare-Earth-Doped Optical Fiber Having Small Numerical Aperture, filed Nov. 11, 2010, (Boivin et al.); U.S. patent application Ser. No. 12/953,948 for a High-Bandwidth, Multimode Optical Fiber with Reduced Cladding Effect, filed Nov. 24, 2010, (Molin et al.); U.S. patent application Ser. No. 12/954,036 for a High-Bandwidth, Dual-Trench-Assisted Multimode Optical Fiber, filed Nov. 24, 2010, (Molin et al.); U.S. patent application Ser. No. 12/959,688 for a Multimode Optical Fiber with Low Bending Losses and Reduced Cladding Effect, filed Dec. 3, 2010, (Molin et al.); U.S. patent application Ser. No. 12/959,866 for a High-Bandwidth Multimode Optical Fiber Having Reduced Bending Losses, filed Dec. 3, 2010, (Molin et al.); U.S. patent application Ser. No. 13/017,089 for a Non-Zero Dispersion Shifted Optical Fiber Having a Large Effective Area, filed Jan. 31, 2011, (Sillard et al.); U.S. patent application Ser. No. 13/017,092 for a Non-Zero Dispersion Shifted Optical Fiber Having a Short Cutoff Wavelength, filed Jan. 31, 2011, (Sillard et al.); U.S. patent application Ser. No. 13/037,943 for a Broad-Bandwidth Multimode Optical Fiber Having Reduced Bending Losses, filed Mar. 1, 2011, (Bigot-Astruc et al.); and U.S. patent application Ser. No. 13/048,028 for a Single-Mode Optical Fiber, filed Mar. 15, 2011, (de Montmorillon et al.).

To supplement the present disclosure, this application further incorporates entirely by reference the following commonly assigned patents, patent application publications, and patent applications: U.S. Pat. No. 5,574,816 for Polypropylene-Polyethylene Copolymer Buffer Tubes for Optical Fiber Cables and Method for Making the Same; U.S. Pat. No. 5,717,805 for Stress Concentrations in an Optical Fiber Ribbon to Facilitate Separation of Ribbon Matrix Material; U.S. Pat. No. 5,761,362 for Polypropylene-Polyethylene Copolymer Buffer Tubes for Optical Fiber Cables and Method for Making the Same; U.S. Pat. No. 5,911,023 for Polyolefin Materials Suitable for Optical Fiber Cable Components; U.S. Pat. No. 5,982,968 for Stress Concentrations in an Optical Fiber Ribbon to Facilitate Separation of Ribbon Matrix Material; U.S. Pat. No. 6,035,087 for an Optical Unit for Fiber Optic Cables; U.S. Pat. No. 6,066,397 for Polypropylene Filler Rods for Optical Fiber Communications Cables; U.S. Pat. No. 6,175,677 for an Optical Fiber Multi-Ribbon and Method for Making the Same; U.S. Pat. No. 6,085,009 for Water Blocking Gels Compatible with Polyolefin Optical Fiber Cable Buffer Tubes and Cables Made Therewith; U.S. Pat. No. 6,215,931 for Flexible Thermoplastic Polyolefin Elastomers for Buffering Transmission Elements in a Telecommunications Cable; U.S. Pat. No. 6,134,363 for a Method for Accessing Optical Fibers in the Midspan Region of an Optical Fiber Cable; U.S. Pat. No. 6,381,390 for a Color-Coded Optical Fiber Ribbon and Die for Making the Same; U.S. Pat. No. 6,181,857 for a Method for Accessing Optical Fibers Contained in a Sheath; U.S. Pat. No. 6,314,224 for a Thick-Walled Cable Jacket with Non-Circular Cavity Cross Section; U.S. Pat. No. 6,334,016 for an Optical Fiber Ribbon Matrix Material Having Optimal Handling Characteristics; U.S. Pat. No. 6,321,012 for an Optical Fiber Having Water Swellable Material for Identifying Grouping of Fiber Groups; U.S. Pat. No. 6,321,014 for a Method for Manufacturing Optical Fiber Ribbon; U.S. Pat. No. 6,210,802 for Polypropylene Filler Rods for Optical Fiber Communications Cables; U.S. Pat. No. 6,493,491 for an Optical Drop Cable for Aerial Installation; U.S. Pat. No. 7,346,244 for a Coated Central Strength Member for Fiber Optic Cables with Reduced Shrinkage; U.S. Pat. No. 6,658,184 for a Protective Skin for Optical Fibers; U.S. Pat. No. 6,603,908 for a Buffer Tube that Results in Easy Access to and Low Attenuation of Fibers Disposed Within Buffer Tube; U.S. Pat. No. 7,045,010 for an Applicator for High-Speed Gel Buffering of Flextube Optical Fiber Bundles; U.S. Pat. No. 6,749,446 for an Optical Fiber Cable with Cushion Members Protecting Optical Fiber Ribbon Stack; U.S. Pat. No. 6,922,515 for a Method and Apparatus to Reduce Variation of Excess Fiber Length in Buffer Tubes of Fiber Optic Cables; U.S. Pat. No. 6,618,538 for a Method and Apparatus to Reduce Variation of Excess Fiber Length in Buffer Tubes of Fiber Optic Cables; U.S. Pat. No. 7,322,122 for a Method and Apparatus for Curing a Fiber Having at Least Two Fiber Coating Curing Stages; U.S. Pat. No. 6,912,347 for an Optimized Fiber Optic Cable Suitable for Microduct Blown Installation; U.S. Pat. No. 6,941,049 for a Fiber Optic Cable Having No Rigid Strength Members and a Reduced Coefficient of Thermal Expansion; U.S. Pat. No. 7,162,128 for Use of Buffer Tube Coupling Coil to Prevent Fiber Retraction; U.S. Pat. No. 7,515,795 for a Water-Swellable Tape, Adhesive-Backed for Coupling When Used Inside a Buffer Tube (Overton et al.); U.S. Patent Application Publication No. 2008/0292262 for a Grease-Free Buffer Optical Fiber Buffer Tube Construction Utilizing a Water-Swellable, Texturized Yarn (Overton et al.); European Patent Application Publication No. 1,921,478 A1, for a Telecommunication Optical Fiber Cable (Tatat et al.); U.S. Pat. No. 7,702,204 for a Method for Manufacturing an Optical Fiber Preform (Gonnet et al.); U.S. Pat. No. 7,570,852 for an Optical Fiber Cable Suited for Blown Installation or Pushing Installation in Microducts of Small Diameter (Nothofer et al.); U.S. Pat. No. 7,646,954 for an Optical Fiber Telecommunications Cable (Tatat); U.S. Pat. No. 7,599,589 for a Gel-Free Buffer Tube with Adhesively Coupled Optical Element (Overton et al.); U.S. Pat. No. 7,567,739 for a Fiber Optic Cable Having a Water-Swellable Element (Overton); U.S. Pat. No. 7,817,891 for a Method for Accessing Optical Fibers within a Telecommunication Cable (Lavenne et al.); U.S. Pat. No. 7,639,915 for an Optical Fiber Cable Having a Deformable Coupling Element (Parris et al.); U.S. Pat. No. 7,646,952 for an Optical Fiber Cable Having Raised Coupling Supports (Parris); U.S. Pat. No. 7,724,998 for a Coupling Composition for Optical Fiber Cables (Parris et al.); U.S. Patent Application Publication No. US2009/0214167 A1 for a Buffer Tube with Hollow Channels, (Lookadoo et al.); U.S. Patent Application Publication No. US2009/0297107 A1 for an Optical Fiber Telecommunication Cable, filed May 15, 2009, (Tatat); U.S. Patent Application Publication No. US2009/0279833 A1 for a Buffer Tube with Adhesively Coupled Optical Fibers and/or Water-Swellable Element, filed Jul. 21, 2009, (Overton et al.); U.S. Patent Application Publication No. US2010/0092135 A1 for an Optical Fiber Cable Assembly, filed Sep. 10, 2009, (Barker et al.); U.S. Patent Application Publication No. US2010/0067857 A1 for a High-Fiber-Density Optical Fiber Cable, filed Sep. 10, 2009, (Louie et al.); U.S. Patent Application Publication No. US2010/0067855 A1 for a Buffer Tubes for Mid-Span Storage, filed Sep. 11, 2009, (Barker); U.S. Patent Application Publication No. US2010/0135623 A1 for Single-Fiber Drop Cables for MDU Deployments, filed Nov. 9, 2009, (Overton); U.S. Patent Application Publication No. US2010/0092140 A1 for an Optical-Fiber Loose Tube Cables, filed Nov. 9, 2009, (Overton); U.S. Patent Application Publication No. US2010/0135624 A1 for a Reduced-Size Flat Drop Cable, filed Nov. 9, 2009, (Overton et al.); U.S. Patent Application Publication No. US2010/0092138 A1 for ADSS Cables with High-Performance Optical Fiber, filed Nov. 9, 2009, (Overton); U.S. Patent Application Publication No. US2010/0135625 A1 for Reduced-Diameter Ribbon Cables with High-Performance Optical Fiber, filed Nov. 10, 2009, (Overton); U.S. Patent Application Publication No. US2010/0092139 A1 for a Reduced-Diameter, Easy-Access Loose Tube Cable, filed Nov. 10, 2009, (Overton); U.S. Patent Application Publication No. US2010/0154479 A1 for a Method and Device for Manufacturing an Optical Preform, filed Dec. 19, 2009, (Milicevic et al.); U.S. Patent Application Publication No. US 2010/0166375 for a Perforated Water-Blocking Element, filed Dec. 29, 2009, (Parris); U.S. Patent Application Publication No. US2010/0183821 A1 for a UVLED Apparatus for Curing Glass-Fiber Coatings, filed Dec. 30, 2009, (Hartsuiker et al.); U.S. Patent Application Publication No. US2010/0202741 A1 for a Central-Tube Cable with High-Conductivity Conductors Encapsulated with High-Dielectric-Strength Insulation, filed Feb. 4, 2010, (Ryan et al.); U.S. Patent Application Publication No. US2010/0215328 A1 for a Cable Having Lubricated, Extractable Elements, filed Feb. 23, 2010, (Tatat et al.); U.S. Patent Application Publication No. US2011/0026889 A1 for a Tight-Buffered Optical Fiber Unit Having Improved Accessibility, filed Jul. 26, 2010, (Risch et al.); U.S. Patent Application Publication No. US2011/0064371 A1 for Methods and Devices for Cable Insertion into Latched Conduit, filed Sep. 14, 2010, (Leatherman et al.); U.S. Patent Publication No. 2011/0069932 A1 for a High-Fiber-Density Optical-Fiber Cable, filed Oct. 19, 2010, (Overton et al.); U.S. Patent Publication No. 2011/0091171 A1 for an Optical-Fiber Cable Having High Fiber Count and High Fiber Density, filed Oct. 19, 2010, (Tatat et al.); U.S. patent application Ser. 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In the specification and/or figures, typical embodiments of the invention have been disclosed. The present invention is not limited to such exemplary embodiments. The use of the term “and/or” includes any and all combinations of one or more of the associated listed items. The figures are schematic representations and so are not necessarily drawn to scale. Unless otherwise noted, specific terms have been used in a generic and descriptive sense and not for purposes of limitation. 

1. A method for curing a coating on a glass fiber, comprising: providing a cavity that defines a curing axis; passing a glass fiber having an incompletely cured coating through the cavity and along the curing axis, the coating having a first absorption peak occurring at a wavelength greater than 300 nanometers, wherein the glass fiber does not possess an incompletely cured coating having an absorption peak that is between 200 nanometers and 300 nanometers; directing UV radiation from a first UV-radiation source to promote the curing of the coating, at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source having wavelengths of between about 200 nanometers and 300 nanometers; and directing UV radiation from a second UV-radiation source to promote the curing of the coating, at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source having wavelengths within 10 nanometers of the coating's first absorption peak.
 2. The method according to claim 1, comprising: directing UV radiation from a third UV-radiation source to promote the curing of the coating, the coating having a second absorption peak occurring at a wavelength greater than 300 nanometers, wherein at least about 80 percent of the electromagnetic radiation emitted by the third UV-radiation source has wavelengths within 10 nanometers of the coating's second absorption peak.
 3. The method according to claim 1, comprising providing a reduced-oxygen environment around the glass fiber as it passes along the curing axis.
 4. The method according to claim 1, comprising providing an oxygen-free environment around the glass fiber as it passes along the curing axis.
 5. The method according to claim 1, comprising providing a heated environment around the glass fiber as it passes along the curing axis.
 6. A method according to claim 1, wherein at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 230 nanometers and 270 nanometers.
 7. The method according to claim 1, wherein at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 245 nanometers and 265 nanometers.
 8. The method according to claim 1, wherein at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths of between about 360 nanometers and 380 nanometers.
 9. The method according to claim 1, wherein at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths of between about 375 nanometers and 395 nanometers.
 10. The method according to claim 1, wherein at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths of between about 390 nanometers and 410 nanometers.
 11. The method according to claim 1, wherein: the coating's first absorption peak occurs at a wavelength greater than 350 nanometers; and the glass fiber does not possess an incompletely cured coating having an absorption peak that is less than 350 nanometers.
 12. A method for curing a coating on a glass fiber, comprising: applying a coating to a glass fiber, the coating having an absorption peak in the UV spectrum between about 300 nanometers and 450 nanometers, wherein the glass fiber does not possess a coating having an absorption peak that is between about 200 nanometers and 300 nanometers; exposing the coating to electromagnetic radiation from a first UV-radiation source to promote curing of the coating, wherein at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 200 nanometers and 300 nanometers; and exposing the coating to UV radiation from the first radiation source or a second UV-radiation source to further promote the curing of the coating, wherein the second UV-radiation source has a mean output wavelength within about 10 nanometers of the coating's absorption peak.
 13. The method according to claim 12, wherein the second UV-radiation source has a mean output wavelength within about 5 nanometers of the coating's absorption peak.
 14. The method according to claim 12, wherein: the coating's first absorption peak occurs at a wavelength between 350 nanometers and 450 nanometers; and the glass fiber does not possess a coating having an absorption peak that is less than 350 nanometers.
 15. The method according to claim 12, comprising directing heated gas around the glass fiber as it passes along the curing axis.
 16. A method for curing a coating on a glass fiber, comprising: applying a coating to a glass fiber, the coating having a first absorption peak that is greater than 300 nanometers and a second absorption peak that is greater than 300 nanometers, wherein the glass fiber does not possess a coating having an absorption peak that is between 200 nanometers and 300 nanometers; exposing the coating to electromagnetic radiation from a first UV-radiation source to promote curing of the coating, wherein at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 200 nanometers and 300 nanometers; exposing the coating to UV radiation from a second UV-radiation source to further promote the curing of the coating, wherein the second UV-radiation source has a mean output wavelength that is within about 10 nanometers of the coating's first absorption peak; and exposing the coating to UV radiation from a third UV-radiation source to further promote the curing of the coating, wherein the third UV-radiation source has a mean output wavelength that is within about 10 nanometers of the coating's second absorption peak.
 17. The method according to claim 16, wherein the second UV-radiation source has a mean output wavelength that is within about 5 nanometers of the coating's first absorption peak.
 18. The method according to claim 16, wherein the third UV-radiation source has a mean output wavelength that is within about 5 nanometers of the coating's second absorption peak.
 19. The method according to claim 16, wherein at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths within a 15-nanometer range.
 20. The method according to claim 16, wherein at least about 80 percent of the electromagnetic radiation emitted by the third UV-radiation source has wavelengths within a 15-nanometer range.
 21. The method according to claim 16, wherein: at least about 80 percent of the electromagnetic radiation emitted by the first UV-radiation source has wavelengths of between about 245 nanometers and 265 nanometers; at least about 80 percent of the electromagnetic radiation emitted by the second UV-radiation source has wavelengths of between about 360 nanometers and 380 nanometers; and at least about 80 percent of the electromagnetic radiation emitted by the third UV-radiation source has wavelengths of between about 390 nanometers and 410 nanometers.
 22. A method according to claim 16, wherein the coating's second absorption peak is at least about 10 nanometers greater than the coating's first absorption peak.
 23. The method according to claim 16, wherein the glass fiber does not possess a coating having an absorption peak that is less than about 350 nanometers. 